An analysis with Valgrind uncovered that the costliest features are mutex locking/unlocking, malloc/no cost and QImage managing. So I did some optimizations concerning QImage. In commit 1f976e5b5ee3cfe40921c74b97edb8d84ff39dd3 I reorganized the Smalltalk bitmap to QImage conversion which resulted in testStandardTests working time of 142 seconds to